THE PINE APPLE. 



157 



stable, or cow-house, would afford an equally ef- 

 ficient, though less delicate, fluid. The ammoniacal 

 gas might, I conceive, be impelled, by means of a 

 pair of bellows, amongst the leaves of the infected 

 plants, in sufficient quantity to destroy animal, 

 without injuring vegetable life : and it is a very in- 

 teresting question to the gardener, whether his 

 hardy enemy, the red spider, will bear it with im- 

 punity." 



In the year 1820, in June, Mr. Knight had such 

 a house as he has hinted at, erected. Its general 

 appearance (fig. 18.), is simple, and the roof ad- 



18 



mits as much light, as any roof that can be con- 

 structed in the present state of knowledge, in the 

 combination of wrought iron and common glass. 

 The plan of this house, or pit (fig. 19- )> is fifty 



feet in length, and ten feet wide ; the furnace ( a ) 



